Method of cooling the hydraulic fluid in the working circuit of a construction machine, in particular a hydraulic excavator

ABSTRACT

A method for cooling hydraulic oil present in an operating circuit of a construction machine, and an installation for cooling hydraulic oil according to the method. The method includes the steps of guiding the hydraulic oil at least partially over an oil cooler and thereafter causing the hydraulic oil to flow into a hydraulic oil tank. The hydraulic oil returning from operating areas of the operating circuit is stored intermediately and has an elevated temperature, the storage occurring in an intermediate reservoir spatially separate from the hydraulic oil present in the hydraulic oil tank prior to causing the hydraulic oil to flow into the hydraulic oil tank. The hydraulic oil is pumped from the intermediate reservoir to the oil cooler for lowering the temperature of the hydraulic oil prior to causing the hydraulic oil to flow into the hydraulic oil tank. The hydraulic oil is then caused to flow into the hydraulic oil tank from the oil cooler for mixing the hydraulic oil flowing into the hydraulic oil tank from the oil cooler with the hydraulic oil present in the hydraulic oil tank. The hydraulic oil flowing into the hydraulic oil tank from the oil cooler has a temperature different from the temperature of the hydraulic oil present in the hydraulic oil tank.

FIELD OF INVENTION

The invention relates to a method for cooling the hydraulic oil presentin the operating circuit of a construction machine, in particular ahydraulic excavator, in that the hydraulic oil is guided at leastpartially over an oil cooler and thereafter flows into a hydraulic oiltank.

BACKGROUND OF THE INVENTION

At present two methods are used for cooling the hydraulic oil inconstruction machines, in particular hydraulic excavators.

According to one method, all partial flows flow into a central tank, inwhich subsequently an appropriate mixing temperature ensues. A partialamount of this hydraulic oil is aspirated by a pump and guided over anoil cooler, which cooperates with a blower motor, before it cause theoil to flow back into the tank. To assure an appropriate operatingtemperature of the hydraulic oil in the tank, it is necessary either toaspirate a large amount of oil out of it or the oil cooler must beembodied to be of an appropriate size.

According to another method defined partial flows are directly led tothe collecting tank and the heated oil from the hydraulic operatingsystem (operating cylinders) is supplied to an oil cooler beforereaching the collecting tank. The advantages of the above are that forthermodynamic reasons, the hottest part of the oil is provided to thecooler part, since in this way a higher cooling output can be achieved.Disadvantages are based on the fact that hydraulic operating system(operating cylinders) of the construction machine is not continuouslyoperated and, therefore the temperature in the collecting tank mayattain critical values.

It is an object of the invention to achieve an optimization of thedegree of efficiency at the hydraulic oil cooler in order to assure inevery case that the temperature present in the collecting tank cannotattain critical values. Further more, it is another object of theinvention to reduce the cooling surface of the oil cooler.

SUMMARY OF THE INVENTION

The above objects are attained in accordance with the invention in thatthe hydraulic oil returning from the operating area(s), in particularthe operating cylinders, having a very high temperature, isintermediately stored prior to entering the hydraulic oil tank, i.e.that it is spatially separated from the oil in the hydraulic oil tank,and is aspirated from there via a pump which sends the hydraulic oilwhich is at a high temperature level to the oil cooler before it flowsback into the hydraulic oil tank at an appropriately lower temperatureand is mixed there with the hydraulic oil of a different temperaturelevel which is present there.

The pump preferably aspirates hydraulic oil from the hydraulic oil tank,if needed through a bypass, as soon as the amount of oil present in theintermediate reservoir falls below a preset filling amount or a presetfilling level. The aspiration of secondary air is prevented by thisstep. In the same way the pump can automatically aspirate the hotterhydraulic oil from the intermediate reservoir when the filling amount orthe filling level are exceeded.

A device for cooling the hydraulic oil present in the operating circuitof a construction machine is distinguished in that a further containerin the form of an intermediate reservoir is provided in the area of thehydraulic oil tank, wherein the container in accordance with a furtherconcept of the invention constitutes a partial area of the hydraulic oiltank. Accordingly, separate components which require structural spacebecome superfluous, particularly since the total oil amount is notchanged and instead is merely provided at different places of thehydraulic oil tank. The hot hydraulic oil provided in the intermediatereservoir is supplied to the oil cooler via a separate aspirating pumpdesigned as a cooling oil pump, wherein this aspirating pumpautomatically aspirates oil from the hydraulic oil tank when there istoo low a filling amount or filling level in the intermediate reservoir.

If a separate bypass line is used, at least one measuring device ispreferably provided in the area of the intermediate reservoir, whichcooperates with an appropriate switching device for redirecting the oilflows from the intermediate reservoir or the hydraulic oil tank.

If, however, no bypass line is to be used, the container disposed in thehydraulic oil tank, which projects into the hydraulic oil tank, can beprovided at its bottom with at least one opening to the space inside thehydraulic oil tank, through which the aspirating pump can aspiratecooler oil from the hydraulic oil tank in case of too low a proportionof hot oil in the intermediate reservoir. In this way it is possible ina simple manner to prevent the aspiration of secondary air or thecreation of a vacuum in the intermediate reservoir.

By means of the method according to the invention, the inlet temperaturedifference of the oil cooler can be greater by approximately 10° K. thanit was possible to achieve by the conventional steps. As a result thecooling surface, depending on the type of the machine, can be reduced byup to 40%, which results in not insignificant savings in cost because ofreduced coolers and a single aspirating installation.

BRIEF DESCRIPTION OF THE DRAWING

The invention is represented in the drawings by an exemplary embodiment.

The single drawing FIGURE shows the method and subject characteristicsof the invention in a top view in the form of a basic diagram.

DETAILED DESCRIPTION OF THE INVENTION

A partial area of the hydraulic operating system 1 is represented, whichin this example is constituted by several operating cylinders 2, 3, 4,5. The hydraulic oil is brought via supply lines 6, 7, 8, 9, which areonly suggested, into the area of the operating cylinders 2, 3, 4, 5, andis removed again via return lines 10, 11, 12, 13. The return lines 10,11, 12, 13 are combined into a collecting or return line 14 and arebrought to a container 15 designed as an intermediate reservoir, whichdips into the oil which is present--which cannot be seen in this topview--in the hydraulic oil tank 16. The intermediate reservoir 15constitutes a partial area of a central hydraulic oil tank 16 and isequipped with elongated filter cartridges 17, 18. Additional returnlines from other areas of the hydraulic system (not further represented)are indicated by lines 19 and 20 which, however, do not supply therespectively flowing hydraulic oil to the intermediate reservoir 15, butdirectly via further filter element 21 to the sump of the hydraulic oiltank 16. The hydraulic oil from the hydraulic operating system 1 flowinginto the intermediate reservoir 15 is aspirated by means of a coolingoil pump 23 through the line 23 and sent to a downstream-connected oilcooler 24. The oil which is cooled here is now forwarded through afurther line 25 through the filters 21 into the sump of the hydraulicoil tank 16. To the extent that the predetermined filling level of thehot hydraulic oil in the intermediate reservoir 15 has not beennegatively exceeded, the cooling oil pump 22 continuously aspirates oilfrom the intermediate reservoir 15 in accordance with its conveyingoutput and provides it via the cooler 24 to the sump of the hydraulicoil tank 16. To the extent that the predetermined filling level wasnegatively exceeded because of the continuous operation of the hydraulicoperating system or when starting the construction machine, oil isaspirated, for example, directly from the sump of the hydraulic oil tankthrough openings (not shown) provided in the lower region of theintermediate reservoir 15. The cooling oil pump 22 therefore does notaspirate any secondary air and can be continuously supplied with oil.

Alternatively there is the option to measure the filling level in theintermediate reservoir 15 via a bypass line 26 and a measuring device26', and to automatically cause a switch by means of switching device26" to a tap point 27 at the hydraulic oil tank 16, wherein theaspirating point 28 at the intermediate reservoir is temporarily closedlong enough until the filling level in the intermediate reservoir 15 hasagain reached its predetermined value.

Furthermore, aspirating lines 29, 30, 31, 32 can also be seen in thedrawing figure which lead on the one side to main operating pumps 33, 34and on the other side to a pilot pump 35 and a swivel pump 36 which inturn cooperate with users, not shown.

What I claim is:
 1. A method for cooling hydraulic oil present in anoperating circuit of a construction machine comprising the stepsof:intermediately storing only a portion of the hydraulic oil returningfrom operating areas of the operating circuit and having an elevatedtemperature in an intermediate reservoir spatially separate from thehydraulic oil present in a hydraulic oil tank prior to causing thehydraulic oil to flow into the hydraulic oil tank; pumping the hydraulicoil having an elevated temperature from the intermediate reservoir to anoil cooler for lowering a temperature of the hydraulic oil prior tocausing the hydraulic oil to flow into the hydraulic oil tank; causingthe hydraulic oil to flow into the hydraulic oil tank from the oilcooler for mixing the hydraulic oil flowing into the hydraulic oil tankfrom the oil cooler with the hydraulic oil present in the hydraulic oiltank, the hydraulic oil flowing into the hydraulic oil tank from the oilcooler having a temperature different from the temperature of thehydraulic oil present in the hydraulic oil tank; and pumping hydraulicoil from the hydraulic oil tank as soon as the hydraulic oil in theintermediate reservoir falls below a predetermined filling level.
 2. Themethod according to claim 1, wherein the construction machine is ahydraulic excavator.
 3. The method according to the claim 1, wherein theoperating areas comprise operating cylinders.
 4. The method according toclaim 1, wherein the step of pumping includes the step of pumping thehydraulic oil from the intermediate reservoir to the oil cooler as soonas the hydraulic oil in the intermediate reservoir exceeds apredetermined filling level.
 5. An installation for cooling hydraulicoil present in an operating circuit of a construction machine accordingto the method of claim 1, comprising an oil cooler and a hydraulic oiltank in flow communication with the oil cooler, wherein the improvementcomprises an intermediate reservoir in flow communication with both thehydraulic oil tank and the oil cooler, the intermediate reservoirconstituting a partial area of the hydraulic oil tank.
 6. Theinstallation according to claim 5, further comprising a pumpstructurally separate from and in flow communication with the oilcooler, the hydraulic oil tank, and the intermediate reservoir, the pumpbeing effective for pumping hydraulic oil from the intermediatereservoir to the oil cooler and for pumping hydraulic oil from thehydraulic oil tank.
 7. The installation according to claim 5, furthercomprising:a first aspirating line leading from the intermediatereservoir to the pump; and a second aspirating line leading from thehydraulic oil tank to the first aspirating line.
 8. An installation forcooling hydraulic oil present in an operating circuit of a constructionmachine according to the method of claim 1, comprising an oil cooler anda hydraulic oil tank in flow communication with the oil cooler, whereinthe improvement comprises:an intermediate reservoir in flowcommunication with both the hydraulic oil tank and the oil cooler; atleast one measuring device operatively associated with the intermediatereservoir; and a switching device operatively associated with the atleast one measuring device for cooperating with the measuring device forredirecting a flow of hydraulic oil from the intermediate reservoir orthe hydraulic oil tank.